Generally, sodium or mercury bulbs are used in extended height applications such as: hotel lobbies, factories, or streetlights. These bulbs have a limited lifecycle of approximately 5000˜6000 hours requiring frequent changing and periodic maintenance. When these lamps (i.e. chandelier) are used in a hotel lobby or wedding hall, they require extra maintenance including cleaning, shining, polishing as well as changing the bulbs to maintain elegant appearance. Maintenance is done using a ladder, increasing the possibility of injury due to accidental fall.
Streetlights are usually located at a height of 7˜10 m, therefore basket bracket installed crane trucks are used during maintenance of the high mounted streetlights. Furthermore, at least three workers are necessary to clean or change the high mount lamp with the crane or the ladder truck of a large size, which constitutes long hours and a very wide working area. For example, a cargo crane generally occupies one or two cranes for maintenance of a streetlight, causing traffic jam and/or accidents. Thus, the maintenance must be prompt.
For high ceiling lamps in a factory line or gymnasium, the production line and/or all activities must be stopped if the maintenance is in progress. To prevent the loss of production and time, maintenance must be done quickly.
If maintenance of the high mounted light bulbs is done improperly, it may cause the following problems: maintenance costs are increased due to the use of expensive equipments, extensive manpower, material damage and human injury with exposure to various dangers including electric shock and falling.
To minimize such problems, there have been developed operating methods and devices for descending a high mounted lamp safety to the ground where the workers are eliminating the need for them to risk climbing or being elevated up to the lamp. Upon the completion of bulb replacement or maintenance, the lamp can be ascended back to its original location.
As a device for ascending and descending a lamp from ceiling to the ground, there are 1) a manual ascending and descending device for a high mounted lamp with a wire is fixed to the lamp, in which the wire is wound around a pulley fixed to the ground so as to ascend and descend the high mounted lamp by a handle bar connected to the pulley, and 2) an automatic ascending and descending device for a high mounted lamp, which includes a motor instead of the handle bar.
The automatic ascending and descending device for a high mounted lamp is generally composed of a socket for fixing the high mounted lamp and fastened to the ceiling, a lamp unit inserted and electrically connected to the socket and having a light bulb mounted at the bottom of the socket, wire with one end fixed to the top of the lamp unit and the other end, with a predetermined length, wound around a drum installed at a certain position of the socket, and a motor for ascending and descending the lamp unit automatically by winding or releasing the wire according to user's request. Several automatic ascending and descending devices of a high mounted lamp are proposed until now, but basic structure deviates little from the above structure.
The most important part of the high mounted lamp ascending/descending device is the electrical contact between the socket and the lamp unit. Unless the socket and the lamp unit are electrically connected accurately, electricity cannot be transmitted to the bulb and the lights will not work, which is the main function of the lamps.
An example of such a contact portion of the high mounted lamp ascending/descending device is proposed in Japanese Patent Laid-open Heisei2-94312. The lamp ascending/descending device revealed in this document is composed of two wires in order to prevent gyration of the lamp unit while ascending or descending. To some extent, this technique may prevent gyration of the lamp unit itself, but has drawbacks of structural complexity and material cost increase because as two sets of the motor, the drum and the wire are needed.
In addition, Japanese Utility Laid-open Showa59-101313 discloses a male-female structure in which an upper socket is tapered at a certain angle to prevent rotation of the lamp unit so that the lamp unit may be guided and then combined into the tapered socket. But, the electrical contact is still not precise and smooth enough.
In the conventional automatic ascending/descending device of a high mounted lamp as described above, the male-female contact points do not contact each other smoothly, so they often need to ascend and descend the lamp unit several times until the contact points are properly contacted.
Due to such a problem, a lot of conventional high mounted lamp ascending/descending devices are not put into practical use in spite of their beneficial function and practicality.